【作者】 贾利军；

【导师】 张怀武；

【作者基本信息】 电子科技大学 ， 材料物理与化学， 2008， 博士

【摘要】 随着通讯技术向高频化方向的发展以及高速数字电路的快速发展,超高频段上的电磁干扰（EMI）问题日益突出,迫切需要能工作在超高频段且性能优异的软磁铁氧体介质材料。其中Z型六角铁氧体由于具有较高的磁晶各向异性,成为最有可能替代尖晶石铁氧体在超高频段应用的磁性介质,有望用作高频片式电感用铁氧体材料和超高频段抗电磁干扰对策元件用微波铁氧体材料。本文正是针对上述问题,以Z型六角铁氧体材料为主要研究对象,在深入分析了合成机理、掺杂改性和低温烧结机制的基础上,对材料和工艺做了探索性和创新性的研究,主要内容为:一、研究了固相反应法合成Z型六角铁氧体的相变过程和反应规律。发现采用片状Co₃O₄制得的粉料在1250～1300℃之间预烧可以获得单一的Z相;随着Sr取代量的增加,出现Z相的预烧温度区间将变窄。二、研究了工艺条件对材料电磁性能的影响机理。按照工艺流程改变预烧温度、升降温速率、烧结温度和保温时间等工艺参数,通过扫描电镜分析、X-射线衍射分析等手段剖析了改变工艺参数对六角铁氧体材料微观结构的影响规律,通过对材料复数磁导率、介电常数以及品质因数等的测量掌握了工艺参数对材料电磁性能的影响规律,根据实验结果对六角铁氧体的制备工艺参数进行了优化。首次提出了利用磁化处理工艺展宽频带的方法,发现特殊微结构的出现是六角铁氧体共振频率向高频方向移动的直接原因。三、研究了不同掺杂剂对Z型六角铁氧体的改性机制。研究了Y₂O₃、Nb₂O₅和Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃（PZTS）含量对Z型六角铁氧体显微结构和电磁性能的影响。发现Y₃Fe₅O₁₂石榴石相的析出改善了六角铁氧体的介电常数和磁导率的频率特性。揭示了Nb₂O₅掺杂引起的磁晶各向异性常数的减小对获得高磁导率的影响机理。发现PZTS掺杂在改善材料介电特性的同时还促进了磁导率的增加。四、研究了Bi₂O₃、Bi₂O₃-SiO₂和Bi₂O₃-CuO掺杂对低温烧结Z型六角铁氧体的作用机理。发现片状Co₃O₄有利于单一Z相的合成和获得高性能低烧Z型六角铁氧体。揭示了Bi₂O₃掺杂对六角铁氧体物相构成、显微结构与电磁性能的影响机理。探讨了Zn取代与(Ba_0.7Sr_0.3)₃Cu_0.5Co_1.5-xZn_xFe₂₄O₄₁（0≤x≤1.5）铁氧体磁性能之间的关系。发现Bi₂O₃-SiO₂掺杂显著改善了Z型六角铁氧体材料的高频电磁特性。五、采用改进的sol-gel法合成超细的六角铁氧体粉料（NZHP）并分析了Z型六角铁氧体的形成过程。研究了掺入由溶胶—凝胶法获得的同成分纳米粉体对固相反应法制备低烧Z型六角铁氧体的改性机理,在没有使用任何添加剂的情况下实现了六角铁氧体的低温烧结。发现含适量NZHP的样品在获得高磁导率的同时拥有较含1.0wt%Bi₂O₃的样品高得多的Q值。更多还原

【Abstract】 With the development of communications technology to high-frequency and the rapid development of high-speed digital circuits,the electromagnetic interference（EMI） is becoming an increasingly serious problem and the excellent soft magnetic materials able to work in the high frequency band are required urgently.Especially,Z-type hexaferrties are among the most widely used soft magnetic materials,instead of spinel ferrite for high-frequency application due to their high magnetic anisotropy.It can be used to the chip inductors for high-frequency and anti-EMI countermeasure devices for ultra-high frequency.In this thesis,the synthesis mechanism and the basic mechanisms of modification and low-temperature sintering of Z-type hexagonal ferrite have been analyzed.Then a series of novel materials and its preparation are explored and investigated.The main results are as follows:1.The phase transition and reaction rules of hexaferrites prepared by a solid-state reaction method were investigated.It was found that,flake Co₃O₄ can be used to achieve single-phase Z-type hexaferrites at 1250-1300℃.With increasing Sr content, the calcination temperature range for Z-type phase will be narrowed.2.The effects of preparation process on the microstructures and electromagnetic properties of hexaferrites and the relative mechanisms were studied in detail.The presintering temperature,firing and cooling rate,sintering temperature,and holding time were changed regularly to investigate the phase formation and the microstructure evolvement of hexaferrites by means of X-ray diffraction（XRD） and scanning electron microscopy（SEM）.The variation of complex permeability,dielectric constant and quality factor with preparation parameters was studied.The effect of premagnetization on the broadband was first proposed.It was found that the special microstructure is the important reason for high resonance frequency.3.The modification mechanisms of different dopants were investigated.The variation of microstructures and electromagnetic properties of hexaferrites with different Y₂O₃,Nb₂O₅ and Pb_0.95Sr_0.05(Zr_0.52Ti_0.48)O₃（PZTS） contents were investigated. The Y₃Fe₅O₁₂ phase was found in all samples with Y₂O₃,resulting in the improvement of electromagnetic properties of hexaferrites.The influence of the reducing K₁ of the samples with Nb₂O₅ on the high permeability was discussed.The additive PZTS improved the complex permeability and the complex permittivity.4.The mechanisms of low-temperature sintering of the hexaferrites with Bi₂O₃,Bi₂O₃-SiO₂ and Bi₂O₃-CuO were investigated.It was found that flake CO₃O₄ is conducive to the synthesis of single Z phase and the preparation of high-performance Z-type hexaferrite sintered at low-temperature.The influence of Bi₂O₃ additive on the phase composition,microstructures and electromagnetic properties of hexaferrties was revealed.The relationship between zinc content and magnetic properties of(Ba_0.7Sr_0.3)₃Cu_0.5Co_1.5-xZn_x Fe₂₄O₄₁（0≤x≤1.5） was discussed.The significant improvement of high-frequency characteristics was obtained for the samples with Bi₂O₃-SiO₂ additive.5.The phase transition and reaction rules of hexaferrites prepared by a improved sol-gel method were investigated.A novel route has been developed to prepare low-temperature sintered Z-type hexaferrites without any additive.The nanoparticles derived an improved sol-gel method were utilized to synthesize the low-temperature fired Z-type hexaferrite by a solid-state reaction method.The higher initial permeability and higher quality factor than that of the sample with 1.0 wt%Bi₂O₃ were obtained for the sample with proper NZHP.更多还原